Friday, December 7, 2018

SCIENCE-PART-2 Pg 16-24

 Page 16
 The spoon acts like a spherical mirror.
 Outer side – acts like convex mirror
 Inner side – acts like concave mirror
 Concave mirror - If the reflecting surface of a spherical mirror is concave, it is called a concave mirror.
 Convex mirror - If the reflecting surface is convex, then it is a convex mirror.
 The image of an object formed by a plane mirror cannot be obtained on screen but it can be obtained in case of concave or convex mirror.
 Real image – an image which can be formed on a screen is called a real image.
 Virtual image – an image which cannot be obtained on a screen is called as virtual image. The image by plain mirror is virtual image.
 In concave mirror the image formed can be smaller or larger in size than the object + it can be real or virtual.
 Uses of concave mirror
o ENT doctor (to examine Ear, nose, Throat)
o Ophthalmologist (to examine eye)
o Dentist (to see an enlarged image of teeth)
o Torch, car, scooter headlight reflectors
 In Convex mirror the object location doesn’t affect the image characteristics and image will always be located behind the convex mirror, a virtual image, an upright image, reduced in size (i.e. smaller than the object)
 Uses of convex mirror
o Side mirror in scooters (with warning - objects in the mirror are closer than they appear)
o Used in places where image of a large area is required
How to remember which mirror has concave and which has convex – Concave is a feeling when your GF/BF says I Love You i.e “:-)” and Convex is when they are with others i.e ‘:-( ” (Hope you get it :P )
Images formed by lenses
 Lens - a curved piece of glass or plastic that makes things look larger, smaller or clearer when you look through it.
 Lens uses –
o Spectacles
o Telescope
o Microscope
o Camera
 Types of lenses
o Concave - thicker in middle

 Page 17
o Convex – thinner in middle
 A convex lens converges (bends inward light generally falling on it and so called as converging lens)
Convex – conve – converge
 A concave lens – diverges (beds outwards) – diverging lens
Sunlight
Rainbow
 A curved shape of different colors seen in the sky when rain is falling and the sun is shining.
 It consists of 7 colors – VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red)
 It appears usually after the rain when the sun is low in the sky,
 We can see a rainbow only when your back is towards the sun.
 A droplet of water in rainbow acts similar to prism.
 The sunlight consists of 7 colors and when it passes through water droplets it gets separated and 7 colors are visible
 If all the 7 colors – VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red) are merged it will result into white color.
Newton disk
 A Newton disc, invented by Isaac Newton, is a disc with seven segments in rainbow colors.
 When the disc is rotated, the colors fade to white; In this way Isaac Newton demonstrated that white light is a combination of the seven different colors found in a rainbow.

 Page 18
 It was an important discovery as it proves that light is not colorless, but has color in it which together converges to give a faded white color which we consider colorless. This property is based on the principles of dispersion of light.
WATER – A PRECIOUS RESOURCE
If you have water, you can think of future)
 22nd March – World Water Day
 UN recommended 30 liters of water per person per day for drinking, washing, cooking and maintaining proper hygiene.
 2003 – International year of freshwater – to make aware people about water.
Q) How much water is available?
 We know that world’s 71% part is of water but still many parts of the world faces acute shortage of water
 Most of the water is in oceans which is not drinkable.
 Only freshwater is drinkable. (freshwater – water that is fit for use)
 In the following figure the teaspoon represents the water available for drinking on the earth (0.006% of all water)

 Page 19
Forms of water
 Water cycle – as the name suggests that it is a cycle in which water keep on moving in different forms (Solid, liquid and eyes)
 Solid – snow and ice caps at poles and snow covered mountains
 Liquid – present in oceans, lakes, rivers and underground.
 Gases – water vapor in air.
 Continuous supply of water in 3 forms keep the total amount of water in earth constant.

 Page 20
 In eater cities the water is provided through water pipelines by civic bodies but it is not the case with rural people. They have to travel several kilometers to fetch water
 Now days this has reduced to some extent and there are wells, tube wells or hand pumps for water access.
Groundwater as an important sources of water
 If we dig deeper and deeper a level would be reached where all the space between particles of soil and gaps between rocks are filled with water.
 Water table – upper limit of this layer is called as water table.
 This level of water table varies i.e. it can be few meters in one place and can be several meters in another place.
 Groundwater – water found below the water table.
Q) How water comes in underground?
 After rain, water seeps into the soil gap or cracks and reaches underground. The process of water into ground – infiltration and so groundwater recharges.
 Aquifer – storing of ground water between 2 hard rock layers below the water table.
 Hand pumps or tube wells are used to pump out water stored in aquifer.
Depletion of water table
 The water drawn from the ground gets recharged by the seepage of rainwater.
 However, if the rate of drawing of water or rate of recharging of water changes it will affect the level of groundwater.
 Other factors which affect the level of groundwater.
o Increase in population
o Increase in industries
o Increase in agriculture activities
o Scanty rainfall
o Deforestation
Increase in population
 Increase in population ? increase demand for food construction of houses, roads etc.
 The construction of roads, homes block or decrease the seepage of rainwater into ground.
 Huge demand of water for construction work.
 Huge demand of water for domestic purpose.
 Above all will result in depletion of groundwater.
Increase in industries
 Industries like paper, tanning, sugarcane etc. uses huge amount of water which affects groundwater level.

 Page 21
Agricultural activities
 Though agricultural uses various canals and rivers water for irrigation but areas where these facilities are not available. They simple dig well, bore well and pump out water for irrigation again affecting water table.
Distribution of water
 Water distribution is uneven over the world. Even in India there are some places like cherrapunji which receives that much rainfall in one day which is received by deserts in whole year.
 Excessive rainfall ? floods
 Absence of rainfall ? Drought
Water management
 Water wastage can be seen at many places. Even sometimes we waste water by opening tap and doing brush instead of using mug.
 Others – leakage, misuse or mismanagement
 We can save water so that it can be used next time or in future
 Rain water harvesting, drip irrigation, water recharge are methods which can help in saving water.
 Explain rainwater harvesting, Bawari and deep irrigation.

 Page 22
FORESTS: OUR LIFELINE
Forests as habitat
 Forests acts as habitat not only for animals but also for many tribal populations.
 They act as home by providing shelter to animals
Forests trees
 There are many trees in the forest.
 The type of trees or vegetation depend on the location of forest.
 In forests – teak, sal, sheesham, neem, semal, palash, fig, khair, amla, bamboo, kachnar, etc. trees are found.
Distinct stratification
 The top layer is captured by long tress which makes thick canopy. It is so much thick that the plants which grow on surface didn’t get enough sunlight.
 The next layer – smaller trees
 Ground - ferns and herbaceous plants
Green lungs
 Forests are also called as green lungs of earth as they purify the impure air by taking CO2 and giving us O2.
 The process is known as photosynthesis. (already covered in chapter 1)
Transpiration
 Trees through transpiration helps in completion of water cycle. (already covered)

 Page 23
 The forest cover induces the rainfall and helping groundwater to recharge again.
Food chain
 Food chain - It may be defined as the transfer of energy and nutrients through a succession of organisms through repeated process of eating and being eaten.
 A food chain starts with producers and ends with top carnivores.
 For example, marsh grass is consumed by grasshopper, the grasshopper is consumed by a bird and that bird is consumed by hawk.
 Thus, a food chain is formed which can be written as follows:
 Marsh grass ----? grasshopper ----? bird ? hawk
 For more details, see environment notes
Humus and decomposers
 Tiny insects, millipedes, ants and beetle feed upon the dead plant and animal tissues and convert them into a dark colored substance called humus.
 The micro-organisms which convert the dead plants and animals to humus are known as decomposers.
 The presence of humus ensures that the nutrients of the dead plants and animals are released into the soil. From there, these nutrients are again absorbed by the roots of the living plants. (recall detritus food chain if you don’t please revise environment notes)
Deforestation effects
 Increased greenhouse gas emissions
o forests help to mitigate carbon dioxide and other greenhouse gas emissions, but they become carbon sources when they are cut, burned or otherwise removed

 Page 24
 Disruption of water cycles
o Trees play a key role in the local water cycle by helping to keep a balance between the water on land and water in the atmosphere.
o But when deforestation or degradation occurs, that balance can be thrown off, resulting in changes in precipitation and river flow.
 Increased soil erosion
o Without trees to anchor fertile soil, erosion can occur and sweep the land into rivers. The agricultural plants that often replace the trees cannot hold onto the soil.
o Many of these plants—such as coffee, cotton, palm oil, soybean and wheat—can actually exacerbate soil erosion.
 Disrupted livelihoods
o Millions of people around the world depend on forests for hunting, gathering and medicine, forest products such as rubber and rattan, and small-scale agriculture. But deforestation disrupts the lives of these people, sometimes with devastating consequences.
 Impacted species
o Most of animals lose their shelter and food.

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